We should strive to be less stupid by studying logical fallacies and cognitive biases. This is helpful in PR, too, since we deal with human communication daily.
Don't let the success of others dictate your strategy. Survivorship bias is a common fallacy; at times it's better to study those who failed.
The principle of scarcity is well-defined in scientific literature. Scarcity makes us want rare things more — simply because they are fewer.